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Abstract:

A conductive paste containing a conductive powder (A), a vinyl
chloride-vinyl acetate resin (B), a polyester resin and/or polyurethane
resin (C), a blocked isocyanate (D) blocked with an active methylene
compound, and an organic solvent (E), wherein the resin (C) has a glass
transition temperature of -50° C. to 20° C., a sum of
amounts of the resin (C) is 50 to 400 parts by weight relative to 100
parts by weight of the resin (B), and a sum of amounts of the resin (B),
the resin (C) component, and the blocked isocyanate (D) is 10 to 60 parts
by weight relative to 100 parts by weight of the conductive powder (A).
An electric wiring in which this conductive paste is formed on an
insulating substrate.

Claims:

1. A conductive paste containing a conductive powder (A), a vinyl
chloride-vinyl acetate resin (B), a polyester resin and/or polyurethane
resin (C), a blocked isocyanate (D) blocked with an active methylene
compound, and an organic solvent (E),wherein the resin (C) has a glass
transition temperature of -50.degree. C. to 20.degree. C.,a sum of
amounts of the resin (C) is 50 to 400 parts by weight relative to 100
parts by weight of the resin (B), anda sum of amounts of the resin (B),
the resin (C) component, and the blocked isocyanate (D) is 10 to 60 parts
by weight relative to 100 parts by weight of the conductive powder (A).

2. The conductive paste of claim 1, wherein a gel fraction ratio of a
soluble solid component within the conductive paste when a heat treatment
at 80.degree. C. and for 30 minutes is applied to the soluble solid
component is 40% to 100%.

3. The conductive paste of claim 1, wherein the resin (B) has been
obtained by copolymerizing components containing a hydroxyl group.

4. The conductive paste of claim 1, wherein an acid value of the resin (B)
is 2 mg KOH/g or less.

5. The conductive paste of claim 1, wherein the conductive powder (A) has
a dendrite structure.

6. An electric wiring comprising an insulating substrate and a film
thereon formed from the conductive paste of claim 1.

7. The electric wiring of claim 6, which further comprises a plated layer.

8. (canceled)

9. (canceled)

10. An electric wiring comprising an insulating substrate and a film
thereon formed from the conductive paste of claim 2.

11. The electric wiring of claim 10, which further comprises a plated
layer.

12. An electric wiring comprising an insulating substrate and a film
thereon formed from the conductive paste of claim 3.

13. The electric wiring of claim 12, which further comprises a plated
layer.

14. An electric wiring comprising an insulating substrate and a film
thereon formed from the conductive paste of claim 4.

15. The electric wiring of claim 14, which further comprises a plated
layer.

16. An electric wiring comprising an insulating substrate and a film
thereon formed from the conductive paste of claim 5.

17. The electric wiring of claim 16, which further comprises a plated
layer.

28. A method of manufacturing an electric wiring, which method comprises
printing and/or applying the conductive paste of claim 1 on an insulating
substrate and then heating the conductive paste to form an electric
wiring on the insulating substrate.

29. A method of manufacturing an electric wiring, which method comprises
printing and/or applying the conductive paste of claim 2 on an insulating
substrate and then heating the conductive paste to form an electric
wiring on the insulating substrate.

30. A method of manufacturing an electric wiring, which method comprises
printing and/or applying the conductive paste of claim 3 on an insulating
substrate and then heating the conductive paste to form an electric
wiring on the insulating substrate.

31. A method of manufacturing an electric wiring, which method comprises
printing and/or applying the conductive paste of claim 4 on an insulating
substrate and then heating the conductive paste to form an electric
wiring on the insulating substrate.

32. A method of manufacturing an electric wiring, which method comprises
printing and/or applying the conductive paste of claim 5 on an insulating
substrate and then heating the conductive paste to form an electric
wiring on the insulating substrate.

Description:

CROSS REFERENCE TO RELATED APPLICATIONS AND INCORPORATION BY REFERENCE

[0001]This application is based upon and claims the benefit of priority
from prior Japanese Patent Application P2008-274230 filed on Oct. 24,
2008; the entire contents of which are incorporated by reference herein.

TECHNICAL FIELD OF THE INVENTION

[0002]The present invention relates to a conductive paste curable at a
lower heating temperature compared to the conductive paste of the related
art. The conductive paste of the present invention has a printability to
pad printing, and also has a printability to various other printing
methods such as screen printing. Also, a coating film formed by the
conductive paste of the present invention has durability to an
electrolytic plating process and to a non-electrolytic plating process.
By performing plating on the coating film, a coating film having a
further higher electric conductivity can be made. Also, an electric
wiring can be formed with a non-plated coating film and/or a plated
coating film, and can be used as an electric circuit such as an antenna
or a shield. In particular, by forming such an electric wiring on a
surface of a housing of an apparatus or appliance, it can greatly
contribute to an improvement in the volume efficiency of the apparatus or
appliance.

BACKGROUND ART

[0003]In accordance with an improvement in the functions, increase in the
number of components of mounted circuit devices is inevitable in mobile
apparatus such as a personal computer, a portable telephone, a fixed
telephone, and a PDA, audio apparatus such as a television set and an
audio player, information terminal apparatus such as an information
management terminal on the point of sale, and home-use electric
appliances such as a cleaner, a refrigerator, an electric rice-cooker,
and an air conditioner. On the other hand, products tend to have smaller
weight, thickness, length, and scale, so that a breakthrough in the
component construction and the mounting method is needed. In order to
solve this problem, it is effective to form an electric circuit also on
the housing for saving space and reduction of the number of components.
In particular, reduction of the mounted antenna volume is demanded in
order to meet the multilateral wireless and multi-resonance communication
of mobile apparatus such as a personal computer or a portable telephone.
If an antenna can be formed directly on a housing, a large volume
reduction effect can be expected. For example, a wireless apparatus is
proposed in which an incorporated type antenna is formed on a housing
(Patent Document 1).

[0004]A technique of forming an electric wiring on a resin member is
generally referred to as the MID (Molded Interconnect Device) method. The
production method is roughly classified into a one-shot method and a
two-shot method depending on the number of times for injection molding of
a resin composition. Also, there are various ones in the two-shot method.
A representative one thereof is the following method. That is, a primary
molded article having a predetermined three-dimensional shape is formed
by injection molding of a resin composition. Next, after surface
roughening of the surface thereof in accordance with the needs, a
secondary molded part is formed to cover a region of the surface of this
primary molded article other than the region where circuits are to be
formed (which may hereafter be referred to as "regions other than the
circuits") by insertion molding, thereby to obtain a so-called two-color
molded article. Next, a state is made in which a catalyst for
non-electrolytic plating is imparted to the entire surface of this
two-color molded article. Then, by performing non-electrolytic plating, a
conductive layer that will be a circuit having a predetermined pattern is
formed in a region on the surface of the primary molded article to which
the catalyst has been selectively imparted, thereby to obtain a MID
(Patent Document 2). This method has a long production lead time by a
complex molding and treating process, and necessitates fabrication of a
plural number of exclusive-use molds, thereby increasing the production
costs. Also, in the case of changing the circuit design, change must be
made starting from a modification of the molds, thereby providing a poor
degree of freedom in designing. Also, the costs will rise, so that this
method is not practical as a method of forming a wiring on a housing that
often tends to have a complex shape.

[0005]On the other hand, a circuit made by printing a conductive paste by
the screen, pad, gravure, flexo, or the like printing on a substrate made
of an insulating material and having various shapes such as a film or a
plate is used in various scenes because of having a small weight and
being capable of forming printed circuits in various places in various
forms. A circuit made from conductive paste alone has a disadvantage of
having a considerably higher specific resistance compared to a
conventional copper foil or aluminum foil; however, this disadvantage is
solved by performing plating on the conductive paste. In recent years,
there is a demand for adopting an insulating substrate such as resin
having a low heat resistance for a printing substrate. The resin that is
commonly used as a housing material of various appliances and apparatus
has a low heat deformation temperature. For example, the PC/ABS resin
(grade MB2215R for portable telephone housing, manufactured by Mitsubishi
Engineering Plastics Co., Ltd.) has a low heat deformation temperature of
92° C., so that a low-temperature curable type conductive paste
that is cured by being heated at a lower temperature than this is
demanded.

[0006]Patent documents 3 and 4 disclose a conductive paste that is
suitable for use as a plating underlayer. The curable system used herein,
which consists of polyester or polyurethane and isocyanate blocked with
an oxime necessitates a heating treatment at about 150° C. in
curing, so that it is difficult to apply this to a substrate having a low
heat resistance such as polycarbonate. Also, it is possible to perform
electrolytic plating that is performed in an acidic plating solution
having a temperature around an ordinary temperature; however, exfoliation
of the coating film may occur in a non-electrolytic plating process that
is exposed to a high temperature and a high alkalinity.

[0007]Patent document 5 discloses a conductive paste of thermoplastic type
that does not contain a curing agent and a conductive paste having a low
curing temperature lowered by compounding a curing catalyst, as a
conductive paste that can form a conductive coating film by a heating
treatment at 80° C. and for 30 minutes. However, both of these use
mainly a polyester resin or a urethane-denatured polyester resin as a
binder resin, so that, when the plating solution has a high temperature
and a high alkalinity, the binder resin may in some cases be deteriorated
to cause exfoliation of the plating immediately after the plating is
performed, so that this may be hardly usable as a conductive paste for a
plating underlayer.

(Patent Documents)

[0008]1. Japanese Patent Application Laid-Open (JP-A) No. 2008-160684

[0009]2. Japanese Patent Application Laid-Open (JP-A) No. 145583/99

[0010]3. Japanese Patent Application Laid-Open (JP-A) No. 293213/96

[0011]4. Japanese Patent Application Laid-Open (JP-A) No. 194768/97

[0012]5. Japanese Patent Application Laid-Open (JP-A) No. 2006-252807

[0013]In view of the above circumstances of the related art, an object of
the present invention is to provide a conductive paste being curable by a
heating treatment at a low temperature of about 80° C. which is
lower than in conventional cases, being capable of withstanding any of
the processes of electrolytic plating and non-electrolytic plating, being
excellent in printability, and being capable of forming an electric
wiring having a further better conductivity by performing plating.

[0014]In order to achieve the above described object, the present
inventors have made eager analyses and studies, and as a result have
found out that a specific conductive paste containing a conductive
powder, an organic resin, a curing agent, and an organic solvent has a
good conductivity and physical property as a coating film while having a
low-temperature curable property, and is excellent in plating property
and a printing property, thereby arriving at the present invention.

[0017]wherein the resin (C) has a glass transition temperature of
-50° C. to 20° C.,

[0018]a sum of amounts of the resin (C) is 50 to 400 parts by weight
relative to 100 parts by weight of the resin (B), and

[0019]a sum of amounts of the resin (B), the resin (C) component, and the
blocked isocyanate (D) is 10 to 60 parts by weight relative to 100 parts
by weight of the conductive powder (A).

[0020]Another aspect of the present invention is the following (2).

[0021](2) A method of manufacturing an electric wiring in which an
electric wiring is formed on an insulating substrate by printing and/or
applying the conductive paste according to (1) on the insulating
substrate, followed by heating.

[0022]The conductive paste of the present invention can form a firm
coating film by a heating treatment of a relatively low temperature. The
formed coating film (coating film not plated yet) exhibits a high
conductivity, exhibits a high close-adhesion property to both of an
insulating substrate having a relatively high heat resistance such as
polyethylene terephthalate, vinyl chloride, or nylon and an insulating
substrate having a relatively low heat resistance such as polycarbonate
or ABS, and exhibits durability (heat resistance, humidity resistance,
heat shock resistance, and coldness resistance) even when exposed to a
severe temperature and humidity environment. Also, by further performing
plating on the coating film not plated yet, a plated coating film
exhibiting a further higher conductivity can be obtained. The coating
film not plated yet is excellent in durability to a highly acidic
treating solution in electrolytic plating and to a highly alkaline
treating solution in non-electrolytic plating, and the plated coating
film exhibits durability (heat resistance, humidity resistance, heat
shock resistance, and coldness resistance) even when exposed to a severe
temperature and humidity environment. In a preferable embodiment, the
conductive paste of the present invention shows a good printability for
various printing methods such as screen printing, pad printing, flexo
printing, and gravure printing, and forms a firm coating film by a
heating treatment of a relatively low temperature, so that the conductive
paste can form a coating film having various shapes at a high speed and
with ease, and hence is suitable for forming an electric wiring on
various insulating substrates. The electric wiring is suitable for use in
an antenna circuit, a sensor circuit, an electromagnetic shield, a
contact point, a heat conduction member, or the like.

BRIEF DESCRIPTIONS OF DRAWINGS

[0023]FIG. 1 is a schematic view illustrating one example of an antenna
pattern according to an embodiment of the present invention;

[0024]FIG. 2 is a schematic view of one example of a pad printing process
according to an embodiment of the present invention;

[0025]FIG. 3 is a flow diagram showing one example of an electrolytic
plating process according to an embodiment of the present invention;

[0026]FIG. 4 is a flow diagram showing one example of a non-electrolytic
plating process according to an embodiment of the present invention;

[0027]FIG. 5 is a schematic view showing one example of a cross section of
a conductive layer according to an embodiment of the present invention;
and

[0028]FIG. 6 is a schematic view of one example of a housing-integrated
type antenna according to an embodiment of the present invention.

DETAILED DESCRIPTION

[0029]As the conductive powder (A) used in the conductive paste of the
present invention, one can use a noble metal powder such as silver
powder, gold powder, platinum powder, or palladium powder, or a base
metal powder such as copper powder, nickel powder, aluminum powder, brass
powder, iron powder, zinc powder, or cobalt powder. Also, it is also
possible to use a base metal powder that has been plated and/or made into
an alloy with use of a noble metal such as silver, or a substance in
which an inorganic filler such as silica, talc, mica, barium sulfate, or
indium oxide is plated with use of a noble metal such as silver. The
conductive powder can be used either alone or as a mixture of different
kinds.

[0030]The shape of the conductive powder is preferably a dendrite
structure in view of the aggregation force to resin. A flaky conductive
powder has a weak aggregation force to resin, and hence is liable to be
exfoliated when plating is performed. Also, a needle structure provides
poor attachment of plating, and can hardly form a uniform circuit.

[0031]The conductive paste having a dendrite structure preferably has an
average particle size (50% D) of 5 to 15 μm as measured by the light
scattering method. More preferably, the average particle size is 8 to 15
μm. When the average particle size is less than 5 μm, the
conductivity may sometimes decrease. On the other hand, when the average
particle size exceeds 15 μm, the surface smoothness may be aggravated,
or a problem such as clogging of the screen template may occur.

[0032]The measurement by the light scattering method as referred to herein
is carried out as follows. A conductive powder is collected with a
microspatula once or twice and is put into a tall beaker of 100 ml.
Thereto is charged about 60 ml of isopropyl alcohol, and the conductive
powder is dispersed for 1 minute with use of a supersonic homogenizer,
and measurement is carried out with use of a microtrack FRA manufactured
by Nikkisoh Co., Ltd. with a measurement time of 30 seconds. For example,
when the conductive powder is silver powder, a measurement is carried out
by assuming the particle refractive index to be 2.25 and the dispersion
medium refractive index to be 1.37.

[0033]Into the conductive paste of the present invention, non-conductive
inorganic fillers such as silica, talc, mica, barium sulfate, and indium
oxide can be compounded. By compounding these, the viscosity and the
thixotropicity of the ink can be raised, whereby the adjustment of the
printability can be made, and a circuit having a fine line pattern can be
formed.

[0034]The vinyl chloride-vinyl acetate resin (B) used in the conductive
paste of the present invention is a copolymer mainly made of vinyl
chloride and vinyl acetate components, and further different kind
components may be copolymerized. A sum content of the vinyl chloride
residue and the vinyl acetate residue of the resin (B) is 50 wt % or
more, further preferably 70 wt % or more, and more preferably 85 wt % or
more relative to the content of the total resin (B). The resin (B) may be
a vinyl chloride-vinyl acetate resin into which different kind components
other than vinyl chloride and vinyl acetate resin are not copolymerized,
or may be a mixture of two or more kinds of vinyl chloride-vinyl acetate
copolymers. When the sum content of the vinyl chloride and the vinyl
acetate is low, the durability to the plating solution tends to decrease.
Also, the number-average molecular weight of the resin (B) is preferably
as high as possible, and is preferably 8,000 or higher, more preferably
10,000 or higher, and further preferably 12,000 or higher. When the
number-average molecular weight is low, the hardness and the close
adhesion property of the coating film tend to decrease. The upper limit
of the number-average molecular weight is not limited; however, it is
preferably 80,000 or lower in view of the solubility.

[0035]Kinds of the different kind copolymerization components of the resin
(B) are not particularly limited; however, it is preferable to
copolymerize acrylic acid, vinyl alcohol, hydroxyethyl acrylate, or the
like to introduce a polar group such as a hydroxyl group or a carboxyl
group. By introduction of a polar group, the paste viscosity can be
raised, whereby the printability tends to be good. Also, when a hydroxyl
group is introduced, a cross-linking reaction takes place by the blocked
isocyanate (D), whereby the durability of the coating film tends to be
improved, so that it is particularly preferable. The hydroxyl value
(hydroxyl number) of the resin (B) is preferably 50 to 100 mgKOH/g. On
the other hand, when a carboxyl group is introduced into the resin (B),
the humidity resistance durability of the plated coating film tends to be
aggravated though the effect of improving the printability is produced.
Therefore, the acid value is preferably 2 mgKOH/g or lower, more
preferably 0.5 mgKOH/g or lower, and further preferably 0.1 mgKOH/g or
lower.

[0036]Specific examples in which different kind components other than
vinyl chloride and vinyl acetate are copolymerized are VMCH manufactured
by Dow Chemical Co., Ltd. in which maleic acid is copolymerized, VAGH
manufactured by Union Carbide Co., Ltd. and TAO manufactured by Nisshin
Chemical Industry Co., Ltd. in which vinyl alcohol is copolymerized, and
VROH manufactured by Union Carbide Co., Ltd. in which hydroxyalkyl
acrylate is copolymerized.

[0037]The resin (C) used in the conductive paste of the present invention
is a polyester resin and/or a polyurethane resin. The resin (C) may be
constituted with one of polyester resin and polyurethane resin alone or
may be a mixture of the two.

[0038]The polyester resin used as the resin (C) of the present invention
preferably has a number-average molecular weight of 10,000 or higher,
more preferably 20,000 or higher, and further preferably 25,000 or
higher. When the number-average molecular weight is 10,000 or lower, the
printability and the plating property tend to decrease. The upper limit
is preferably 100,000 or lower in view of the problems of polymerization
technique. The reduced viscosity of the above described polyester resin
is preferably 0.3 dl/g or higher, more preferably 0.5 dl/g or higher, and
further preferably 0.7 dl/g or higher. The glass transition temperature
(Tg) of the polyester resin is preferably 20° C. or lower, and
more preferably 0° C. or lower. Also, the glass transition
temperature is preferably -50° C. or higher. When the glass
transition temperature is lower than -50° C., the paste coating
film will be soft and the resistance to the plating solution will be
poor. Also, when the glass transition temperature is above 20° C.,
the coating film mixed with vinyl chloride-vinyl acetate resin cannot
fully ensure the close adhesion property to the substrate. The polyester
resin is polymerized by a known method such as the ester exchange method
or the direct polymerization method.

[0039]Also, the polyester resin is preferably one in which aromatic
dicarboxylic acid is contained at 70 mol % or more, and more preferably
80 mol % or more among the total acid components. When aromatic
dicarboxylic acid is contained at less than 70 mol %, the strength of the
coating film decreases, and the durability such as heat resistance,
humidity resistance, and heat shock resistance may possibly decrease. A
preferable upper limit of aromatic dicarboxylic acid is 100 mol %.

[0040]Further, the aromatic dicarboxylic acid that is copolymerized with
the polyester resin may be, for example, terephthalic acid, isophthalic
acid, orthophthalic acid, 2,6-naphthalenedicarboxylic acid, or the like.
Among these, it is preferable to use terephthalic acid and isophthalic
acid in combination in view of the strength of the coating film to be
formed and the solvent solubility of the polyester resin.

[0042]Also, trivalent or polyvalent carboxylic acid such as trimellitic
anhydride or pyromellitic anhydride or unsaturated dicarboxylic acid such
as fumaric acid may be used in combination within a range that does not
deteriorate the object of the invention.

[0043]For the glycol component that is copolymerized with the polyester
resin, a known glycol shown in the following can be suitably used. The
glycol component may be, for example, aliphatic glycol such as ethylene
glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol,
1,5-pentanediol, 1,6-hexanediol, 1,3-butylene glycol, 2,3-butylene
glycol, 2,2-dimethyl-1,3-propanediol, 3-methyl-1,5-pentanediol,
2,2-dimethyl-3-hydroxypropyl-2',2'-dimethyl-3-hydroxypropanate, or
2,2-diethyl-1,3-propanediol, alicyclic glycol such as
1,3-bis(hydroxymethyl)cyclohexane, 1,4-bis(hydroxymethyl)cyclohexane,
1,4-bis(hydroxyethyl)cyclohexane, 1,4-bis(hydroxypropyl)cyclohexane,
1,4-bis(hydroxymethoxy)cyclohexane, 1,4-bis(hydroxyethoxy)cyclohexane,
2,2-bis(4-hydroxymethoxycyclohexyl)propane,
2,2-bis(4-hydroxyethoxycyclohexyl)propane,
bis(4-hydroxycyclohexyl)methane, 2,2-bis(4-hydroxycyclohexyl)propane, or
3(4),8(9)-tricyclo[5.2.1.02,6]decanedimethanol, polyether diol such as
diethylene glycol, polyethylene glycol, or polytetramethylene glycol,
alkylene oxide adduct of bisphenol A, alkylene oxide adduct of bisphenol
F, or the like. Also, trivalent or polyvalent polyol such as trimethylol
ethane, trimethylol propane, glycerin, pentaerythritol, or polyglycerin
may be used in combination. Among these, as the one that lowers the glass
transition temperature, alkylene glycol such as 1,5-pentanediol,
1,6-hexanediol, 3-methyl-1,5-pentanediol, 2-methyl-1,5-pentanediol,
1,9-nonanediol, or 1,10-decanediol is particularly preferable.

[0044]It is preferable that the polyester resin does not have a melting
point (exhibiting a property of being amorphous) in view of adhesiveness
and solvent solubility. The term "does not have a melting point" as used
herein means that the resin does not show a definite melting peak in
differential scanning calorimetry (DSC) analysis.

[0045]The polyurethane resin used as the resin (C) of the present
invention is preferably a polyester urethane resin in view of close
adhesiveness and humidity resistance. A preferable component of the
polyester diol used in synthesizing the polyester urethane resin is the
same as the polyester resin that can be compounded as the already
described resin (C); however, the number-average molecular weight is
preferably 10,000 or higher, and the upper limit is preferably 80,000 or
lower, and more preferably 50,000 or lower. The glass transition
temperature (Tg) of the polyurethane resin is preferably 20° C. or
lower, and more preferably 0° C. or lower. Also, the glass
transition temperature is preferably -50° C. or higher. When the
glass transition temperature is lower than -50° C., the paste
coating film will be soft and the resistance to the plating solution will
be poor. Also, when the glass transition temperature is above 20°
C., the coating film mixed with vinyl chloride-vinyl acetate resin cannot
fully ensure the close adhesion property to the substrate. The
polyurethane resin is synthesized by a known method by compounding
various polyols, a diisocyanate compound, and, if needed, a chain
extending agent. The polyurethane resin can be polymerized in a solution,
thereby having a characteristic capable of obtaining those having a
higher molecular weight compared to polyester resin, and having a
tendency of being able to obtain a high close adhesiveness of the coating
film.

[0047]The resin (C) of the present invention may be any one of a mixture
of two or more kinds of polyester resin, a mixture of two or more kinds
of polyurethane resin, and a mixture of one kind or two or more kinds of
polyester resin and one kind or two or more kinds of polyurethane resin.
The sum of the amounts of the resin (C) in the present invention is
assumed to refer to a sum of the amounts of the total polyester resins
and the total polyurethane resins contained in the conductive paste of
the present invention. The sum of the amounts of the resin (C) is 50 to
400 parts by weight, preferably 55 to 300 parts by weight, and further
preferably 60 to 250 parts by weight relative to 100 parts by weight of
the resin (B). When the sum of the amounts of the resin (C) is less than
50 parts by weight, the close adhesiveness to the substrate tends to
decrease, whereas when the sum exceeds 400 parts by weight, the
resistance to the plating solution tends to decrease.

[0048]The kind of the organic solvent (E) used in the conductive paste of
the present invention is not particularly limited, and may be, for
example, ester type, ketone type, ether ester type, chlorine type,
alcohol type, ether type, hydrocarbon type, or the like. In the case of
performing screen printing, a high-boiling-point solvent such as
ethylcarbitol acetate, butyl cellosolve acetate, isophorone,
cyclohexanone, γ-butyrolactone, DBE (manufactured by Invista Japan
Co., Ltd.), N-methyl-2-pyrrolidone, or monoalkyl ether acetate of
propylene glycol. A preferable boiling point of the solvent is
130° C. or higher, more preferably 150° C. or higher, and
most preferably 180° C. or higher. The upper limit of the boiling
point is preferably 250° C. or lower in view of the drying speed.

[0049]It is necessary that the conductive paste of the present invention
is compounded with blocked isocyanate (D) that has been blocked by an
active methylene compound. Accordingly, a cured coating film can be
obtained by a heating treatment at a relatively low temperature. In a
preferable embodiment, a cured coating film capable of withstanding a
high-temperature and highly alkaline non-electrolytic plating process can
be obtained by a heating treatment at 80° C. and for 30 minutes. A
preferable amount of compounding the blocked isocyanate (D) is 1 to 40
parts by weight relative to 100 parts by weight of the sum of the amounts
of the resin (B) and the resin (C).

[0050]The isocyanate compound that is blocked by an active methylene
compound may be, for example, aromatic, aliphatic, alicyclic
diisocyanate, or trivalent or polyvalent polyisocyanate, and may be
either a low-molecular-weight compound or a high-molecular-weight
compound. For example, it may be a terminal isocyanate group-containing
organic compound obtained by allowing tetramethylene diisocyanate,
hexamethylene diisocyanate, toluene diisocyanate, diphenylmethane
diisocyanate, hydrogenated diphenylmethane diisocyanate, xylylene
diisocyanate, hydrogenated xylylene diisocyanate, isophorone
diisocyanate, or a trimer of these isocyanate compounds and an excessive
amount of these isocyanate compounds to react with a low-molecular-weight
active hydrogen compound such as ethylene glycol, propylene glycol,
trimethylolpropane, glycerine, sorbitol, ethylene diamine,
monoethanolamine, diethanolamine, or triethanolamine or a
high-molecular-weight active hydrogen compound of various polyester
polyols, polyether polyols, and polyamides. The isocyanate compound is
preferably toluene diisocyanate, diphenylmethane diisocyanate, isophorone
diisocyanate, hexamethylene diisocyanate or a derivative thereof in view
of the resistance to plating solution.

[0051]The active methylene compound used as an agent for forming blocked
isocyanate may be, for example, malonic acid dialkyl esters, acetoacetic
acid esters such as methyl acetoacetate or ethyl acetoacetate,
β-diketones such as acetylacetone, or the like, or may be a mixture
of these. The alkyl group in the malonic acid dialkyl esters may be, for
example, methyl, ethyl, isopropyl, n-butyl, iso-butyl, sec-butyl,
tert-butyl, 2-ethylhexyl or the like, and the two alkyl groups may be the
same or different.

[0053]Into the conductive paste of the present invention, a curing
catalyst other than an isocyanate compound may be compounded. As the
curing catalyst, it is preferable to use a tin-type compound in view of
the curability. The tin-type compound may be, for example, dibutyltin
diacetate, dibutyltin dilaurate, dibutyltin mercaptide, dibutyltin
thiocarboxylate, dibutyltin dimaleate, dioctyltin mercaptide, dioctyltin
thiocarboxylate, or the like.

[0054]A curing catalyst other than the tin-type compound may be, for
example, bismuth-type compound such as bismuth-2-ethyl hexanoate or
bismuth neodecanoate, zinc-type compound such as zinc neodecanoate,
monoamine such as triethylamine or N,N-dimethylcyclohexylamine, diamine
such as N,N,N',N'-tetramethylethylenediamine,
N,N,N',N'-tetramethylpropane-1,3-diamine, or
N,N,N',N'-tetramethylhexane-1,6-diamine, triamine such as
N,N,N',N'',N''-pentamethyldiethylenetriamine,
N,N,N',N'',N''-pentamethyldipropylenetriamine, or tetramethylguanidine,
cyclic amine such as triethylenediamine, N,N'-dimethyl piperazine,
N-methyl-N'-(2-dimethylamino)ethylpiperazine, N-methylformalin,
N--(N',N'-dimethylaminoethyl)-morpholine, or 1,2-dimethylimidazole,
alcohol amine such as dimethylaminoethanol, dimethylaminoethoxyethanol,
N,N,N'-trimethylaminoethylethanolamine,
N-methyl-N'-(2-hydroxyethyl)-piperazine, or N-(2-hydroxyethyl)morpholine,
ether amine such as bis(2-dimethylaminoethyl)ether, ethylene glycol
bis(3-dimethyl)-aminopropyl ether, or the like.

[0055]Regarding the amount of compounding the curing catalyst, the lower
limit is preferably 0.05 wt % or more, and more preferably 0.2 wt % or
more relative to the resin (B) in view of the curability, and the upper
limit is preferably 5 wt % or less, and more preferably 3 wt % or less in
view of the problem of decrease in the coating film physical property
such as conductivity.

[0056]A sum of the amounts of the resin (B), the resin (C) component, and
the blocked isocyanate (D) is 10 to 60 parts by weight, more preferably
15 to 45 parts by weight, and further preferably 20 to 40 parts by weight
relative to 100 parts by weight of the conductive powder (A). When the
sum is less than 10 parts by weight, the close adhesiveness to the
substrate tends to be considerably aggravated, whereas when the sum
exceeds 60 parts by weight, the close adhesiveness at the boundary
between the paste and the plating tends to be aggravated after the
plating is carried out.

[0057]The conductive paste of the present invention is preferably such
that the gel fraction ratio of a soluble solid component within the
conductive paste when a heating treatment at 80° C. and for 30
minutes is applied to the soluble solid component is 40% or more, more
preferably 55% or more, and further preferably 70% or more. The upper
limit of the gel fraction ratio is preferably 100% or less. When the gel
fraction ratio is too low, the close adhesiveness of the coating film
after non-electrolytic plating tends to be inferior. Here, in the process
of manufacturing a coating film and an electric wiring, the treatment is
not limited to a heating treatment at 80° C. and for 30 minutes,
so that the temperature may be lower than or higher than 80° C.,
and the heating time may be more than or less than 30 minutes.

[0058]To the conductive paste of the present invention, a known additive
such as defoaming agent, leveling agent, dispersing agent, or coupling
agent is preferably added.

[0059]The defoaming agent may be, for example, a known one such as
silicone resin, silicone solution, special foam-breaking agent that does
not contain silicone, acrylic acid alkyl ester copolymer, methacrylic
acid alkyl ester copolymer, alkyl vinyl ether, acrylic copolymer,
foam-breaking polymer, polysiloxane, foam-breaking polysiloxane,
polymethylalkylsiloxane, polyether denatured polysiloxane, or paraffin
mineral oil. A preferable upper limit of the amount of addition of the
defoaming agent is 2 wt % relative to the paste, and the lower limit is
0.05 wt %. When the amount is less than 0.05 wt %, the effect as a
defoaming agent may not be obtained, whereas when the amount exceeds 2 wt
%, the effect is saturated. This not only is uneconomical but also may
possibly cause decrease in the close adhesiveness or the aggravation of
the anti-blocking property.

[0060]The leveling agent may be, for example, polyether denatured
polydimethylsiloxane, polyester denatured polydimethylsiloxane, polyester
denatured methylalkylpolysiloxane, polyether denatured
polymethylalkylsiloxane, aralkyl denatured polymethylalkylsiloxane,
polyester denatured hydroxyl group-containing polydimethylsiloxane,
polyetherester denatured hydroxyl group-containing polydimethylsiloxane,
acrylic copolymer, methacrylic copolymer, polyether denatured
polymethylalkylsiloxane, acrylic acid alkyl ester copolymer, methacrylic
acid alkyl ester copolymer, acrylic acid, acrylic acid alkyl copolymer, a
graft copolymer of polyoxyalkylenemonoalkyl or alkenyl ether, or
lecithin. A preferable upper limit of the amount of addition of the
leveling agent is 2 wt % relative to the paste, and the lower limit is
0.05 wt %. When the amount is less than 0.05 wt %, the effect as a
leveling agent may not be obtained, whereas when the amount exceeds 2 wt
%, the effect is saturated. This not only is uneconomical but also may
possibly cause decrease in the close adhesiveness or the aggravation of
the anti-blocking property.

[0061]As the dispersing agent, it is possible to use a commercially
available one such as long-chain polyamide type, phosphoric acid salt of
long-chain polyamide, polyamide type, unsaturated polycarboxylic acid, or
tertiary amino group containing polymer. A preferable upper limit of the
amount of addition of the dispersing agent is 2 wt % relative to the
paste, and the lower limit is 0.05 wt %. When the amount is less than
0.05 wt %, the effect as a dispersing agent may not be obtained, whereas
when the amount exceeds 2 wt %, the effect is saturated. This not only is
uneconomical but also may possibly cause decrease in the close
adhesiveness or the aggravation of the anti-blocking property.

[0062]As the coupling agent, it is possible to use a commercially
available one such as aluminum type coupling agent such as alkyl
acetoacetate aluminum diisopropylate, acylate, phosphate, alcoholate, or
a titanate coupling agent of coordinate type. A preferable upper limit of
the amount of addition of the coupling agent is 5 wt % relative to the
paste, and the lower limit is 0.05 wt %. When the amount is less than
0.05 wt %, the effect as a coupling agent may not be obtained, whereas
when the amount exceeds 5 wt %, the effect is saturated. This not only is
uneconomical but also may possibly cause decrease in the close
adhesiveness or the aggravation of the anti-blocking property.

[0063]An electric wiring can be formed by forming a coating film made of
the conductive paste of the present invention on an insulating substrate.
The material of the insulating substrate on which the electric wiring is
formed is not particularly limited; however, an insulating substrate
having a low heat resistance such as PC (polycarbonate), ABS
(acrylonitrile•butadiene•styrene), or PPE (polyphenylene
ether) is preferable. This is because these insulating substrates are
inexpensive and are excellent in molding processability and shock
resistance. Also, the heat resistance as referred to herein is evaluated
on the basis of the load deflection temperature, and a material having a
high load deflection temperature is assumed to be a material having a
high heat resistance, whereas a material having a low load deflection
temperature is assumed to be a material having a low heat resistance. The
load deflection temperature is determined by the temperature (unit:
° C.) at which the magnitude of the deflection attains a constant
value while the temperature of the sample is being raised in a state in
which a load determined by the standard of an industrial testing method
is given. Here, the industrial testing method may be, for example, JIS or
ASTM. The PC is a thermoplastic plastic produced by using bisphenol A and
phosgene (or diphenyl carbonate) as source materials. In the present
invention, for example, the PC (trade name: Iupilon (registered
trademark) grade S-3000R) manufactured by Mitsubishi Engineering Plastic
Co., Ltd. can be used, and the load deflection temperature thereof is
123° C. The ABS is made of a copolymerized synthesized resin of
acrylonitrile, butadiene, and styrene. In the present invention, for
example, the ABS (trade name: Toyolac (registered trademark) grade 250)
manufactured by Toray Co., Ltd. can be used, and the load deflection
temperature thereof is 87° C. The PPE is a thermoplastic resin
having an aromatic polyether structure, and is mainly made into an alloy
with other synthesized resins such as shock-resistant polystyrene to be
used as denatured polyphenylene ether m-PPE. In the present invention,
for example, the PPE (trade name: Iupiace (registered trademark) grade
TX430) manufactured by Mitsubishi Engineering Plastic Co., Ltd. can be
used, and the load deflection temperature thereof is 92° C.
Insulating substrates having a low heat resistance such as these PC, ABS,
and PPE are inexpensive materials, and are excellent in molding
processability and shock resistance. With a conventional conductive
paste, a coating film must be formed by performing a treatment at a high
temperature in order to form an electric wiring or the like, so that the
insulating substrates having a low heat resistance such as PC, ABS, and
PPE could not be used. In contrast, with use of the conductive paste of
the present invention, the coating film can be formed at a low
temperature, so that an electric wiring can be formed on an insulating
substrate being inexpensive and being excellent in molding processability
and shock resistance such as PC, ABS, or PPE. Also, in the present
invention, the insulating substrate may be a mixture or an alloy of a
plurality of resins, or may be one mixed with an insulating filler.

[0064]The electric wiring of the present invention can be produced by a
method of printing and/or applying a conductive paste on an insulating
substrate such as a resin housing molded by ordinary injection molding,
drying and curing the conductive paste by a heating treatment, and
performing non-electrolytic plating or electrolytic plating in accordance
with the needs so as to form a conductive layer. Such a method enables
mass production of electric wirings in a simple manner and at a low cost.

[0065]The method of printing and/or applying the conductive paste may be
various printing and applying methods such as pad printing, screen
printing, ink jet printing, dispenser application, dot dispenser
application, and spray coating application. In particular, the pad
printing method has advantages such that printing can be made on a curved
surface of a housing with ease and, in the case of change in the circuit
design, it can meet the change simply by modifying the template used in
the pad printing, thereby providing a high degree of freedom in
designing. Therefore, the pad printing method is an especially preferable
printing method in the production of electrical wirings of the present
invention. Also, in the case of adopting the pad printing method, the
material of the pad is not particularly limited; however, a suitable
example of the material is silicone rubber. One example of the process of
forming an antenna pattern 11 shown in FIG. 1 by pad printing is shown in
FIG. 2. Here, first, a (desired) antenna pattern 21 made of the
conductive paste is prepared, and then this antenna pattern 21 is printed
(first printing) on the convex part of the pad 22, and thereafter the
antenna pattern 21 on the convex part of the pad 22 is printed (second
printing) at a predetermined position on an insulating substrate 23 such
as a housing.

[0066]The method of drying and curing the printed conductive paste is not
particularly limited; however, it can be carried out by known means such
as a box oven or a conveyor furnace. Also, as a supply source of heat,
known means can be adopted such as electric heating wire, hot air
circulation, or an infrared lamp. The heating temperature and the heating
time are not particularly limited; however, they must be determined by
considering not only the curability of the conductive paste but also the
heat resistance of the insulating substrate. In order to take advantage
of the low-temperature curing property of the conductive paste of the
present invention, it is preferable to carry out a heating treatment at
60 to 100° C. A preferable condition for the heating treatment may
be, for example, a keep time of 3 minutes at 80° C. or a keep time
of 10 minutes at 70° C. in a conveyor type IR furnace, or a keep
time of 30 minutes at 80° C. or a keep time of 60 minutes at
70° C. in a hot air circulation type conveyor furnace.

[0067]The electric wiring in which a conductive paste coating film is
formed on an insulating substrate is preferably further subjected to a
plating process. The plated layer may be formed by electrolytic plating
alone, by non-electrolytic plating alone, or by a process in which
electrolytic plating and non-electrolytic plating are combined. One
example of the electrolytic plating process is shown in FIG. 3, and one
example of the non-electrolytic plating process is shown in FIG. 4. The
electrolytic plating process shown in FIG. 3 is carried out in the order
from (1) through to (12).

[0068](1) An object of plating is immersed into a degreasing liquid, so as
to perform degreasing.

[0069](2) Next, the resultant is washed with cleaning water.

[0070](3) Next, in order to remove oxide film of the conductive powder
contained in the conductive paste of the present invention, the resultant
is immersed into an acid active treating solution.

[0071](4) Next, the resultant is washed with cleaning water.

[0072](5) Next, the resultant is immersed into an electrolytic Cu plating
solution, and an electric current is applied to the conductive paste
layer serving as an object of plating, so as to deposit Cu.

[0073](6) Next, the resultant is washed with cleaning water.

[0074](7) Next, in order to remove oxide film of the Cu plated film, the
resultant is immersed into an acid active treating solution.

[0075](8) Next, the resultant is washed with cleaning water.

[0076](9) Next, the resultant is immersed into an electrolytic Ni plating
solution, and an electric current is applied to the Cu plated layer, so
as to deposit Ni.

[0077](10) Next, the resultant is washed with cleaning water.

[0078](11) Next, the resultant is immersed into an electrolytic Au plating
solution, and an electric current is applied to the Ni plated layer, so
as to deposit Au.

[0079](12) Next, the resultant is washed with cleaning water.

[0080]Also, the non-electrolytic plating process shown in FIG. 4 is
carried out in the order from (1) through to (16).

[0081](1) An object of plating is immersed into a degreasing liquid, so as
to perform degreasing.

[0082](2) Next, the resultant is washed with cleaning water.

[0083](3) Next, in order to remove oxide film of the conductive powder
contained in the conductive paste of the present invention, the resultant
is immersed into an acid active treating solution.

[0084](4) Next, the resultant is washed with cleaning water.

[0085](5) Next, the resultant is immersed into a catalyst imparting
treating solution in order to impart a catalyst.

[0086](6) Next, the resultant is washed with cleaning water.

[0087](7) Next, the resultant is immersed into a non-electrolytic Cu
plating solution to deposit Cu.

[0088](8) Next, the resultant is washed with cleaning water.

[0089](9) Next, the resultant is immersed into a catalyst imparting
treating solution in order to impart a catalyst.

[0090](10) Next, the resultant is washed with cleaning water.

[0091](11) Next, in order to prevent deposition outside of the pattern,
the resultant is immersed into a post-activator treating solution to
remove the catalyst adhering to the outside of the pattern.

[0092](12) Next, the resultant is washed with cleaning water.

[0093](13) Next, the resultant is immersed into a non-electrolytic Ni
plating solution to deposit Ni.

[0094](14) Next, the resultant is washed with cleaning water.

[0095](15) Next, the resultant is immersed into a non-electrolytic Au
plating solution to deposit Au.

[0096](16) Next, the resultant is washed with cleaning water.

[0097]The construction of the plated layer that is formed by performing
electrolytic plating and non-electrolytic plating is not particularly
limited; however, the construction of FIG. 5 can be mentioned as a
preferable example of the case of forming particularly the plated layer
as an antenna circuit. In FIG. 5, on an insulating substrate 31 serving
as a housing, first a coating film 32 formed from the conductive paste
and subsequently each film of Cu 33, Ni 34, and Au 35 are sequentially
formed, so as to form a plated layer made of three films. A preferable
example of the construction of the plated layer may further be Cu,
Ni/Cu/Ni, and Ni/Cu/Ni/Au. Also, the film thickness of each layer is not
particularly limited.

[0098]The electric wiring of the present invention can be used as an
electric circuit, an antenna circuit, a sensor circuit, an
electromagnetic shield, a contact point, a heat conduction member, or the
like. The apparatus of the present invention can be mounted on mobile
apparatus such as a personal computer, a portable telephone, a fixed
telephone, and a PDA, audio apparatus such as a television set and an
audio player, information terminal apparatus such as an IC card, an IC
tag, and an information management terminal on the point of sale, and
home-use electric appliances such as a cleaner, a refrigerator, an
electric rice-cooker, and an air conditioner. Also, since the electric
wiring can be formed along a curved shape, it can contribute to an
improvement in the volume efficiency of these without hindering the
degree of freedom in designing.

EXAMPLES

[0099]The present invention will now be illustrated by using the following
Examples although the present invention is not limited thereto. The term
"part(s)" used in the Examples is one by weight. Also, each measurement
item in the Examples is performed as follows.

[0100]1. Resin Composition

[0101]The resin was dissolved into chloroform-d, and 1H-NMR analysis was
carried out using nuclear magnetic resonance analyzer (NMR) Gemini-200
manufactured by Valian Co., Ltd. and the resin composition was determined
by the integrated ratio thereof.

[0102]2. Reduced Viscosity of Polyester Resin and Polyurethane Resin

[0103]Measurement was carried out at 30° C. by using an Ubbellohde
viscometer after dissolving 0.10 g of the sample into 25 ml of mixed
solvent of phenol/tetrachloroethane (weight ratio=6/4). The unit is
denoted by dl/g.

[0104]3. Number-Average Molecular Weight

[0105]By using a gel filtration permeation chromatograph (GPC) 150c
manufactured by Waters Co., Ltd. using tetrahydrofuran as a moving phase,
GPC measurement was carried out with a column temperature of 30°
C. and a flow rate of 1 ml/min. By calculating from the result thereof, a
measurement value as converted in terms of polystyrene was obtained.
Here, the column that was put to use was shodex KF-802, 804, 806
manufactured by Showa Denko Co., Ltd.

[0106]4. Glass Transition Temperature (Tg)

[0107]With use of a differential scanning calorimeter (DSC), measurement
was carried out at a temperature raising speed of 20° C./min. As a
sample, 5 mg of the sample was put into an aluminum pressing lid type
container, and climped.

[0108]5. Acid Value (mgKOH/g)

[0109]The sample (0.2 g) was precisely weighed, and was dissolved into 20
ml of chloroform. Subsequently, titration was carried out with use of
potassium hydroxide (ethanol solution) of 0.01N, so as to determine the
acid value. As an indicator, phenolphthalein was used.

[0110]6. Hydroxyl Value (mgKOH/g)

[0111]Into 120 g of 2-butanone, 50 g of the resin was dissolved, and 50 g
of diphenylmethane-4,4'-diisocyanate was added, so as to carry out
reaction at 80° C. for 2 hours. Subsequently, the residual
isocyanate group concentration in the reaction liquid was quantitated by
titration, and the result was converted into a hydroxyl value assuming
that the amount of consumed isocyanate is the amount of hydroxyl group
contained in the resin.

[0112]7. Viscosity of the Paste

[0113]The viscosity of the conductive paste was measured with use of a
Brookfield viscometer HBDV type at a rotation speed of 20 rpm at
25° C.

[0114]8. Formation of a Test Piece

[0115]The conductive paste was screen-printed on an insulating substrate
made of PET film having a thickness of 100 μm and treated by annealing
(150° C., 2 hours) into a pattern having a width of 350 mm and a
length of 450 mm (for heat resistance measurement, humidity resistance
measurement, and heat shock resistance property) and into a pattern
having a width of 25 mm and a length of 50 mm (for specific resistance
measurement) so that the film thickness after drying would be 8 to 15
μm. This was dried in a box oven under a condition at 80° C.
and for 30 minutes, thereby to form a test piece.

[0116]9. Specific Resistance

[0117]The test piece prepared in 8. was mounted on a self-made electrode
so that the printed surface would be on the electrode side, and was
pressed with use of a clip for office use. Next, in the case of silver
paste, the upper part of the electrode was connected to a four-probe
resistance measurement device (milliohm meter 4328A type manufactured by
Yokokawa Hewlett Packard Co., Ltd.) with an alligator clip and a copper
wire, so as to measure the sheet resistance. Separately, the film
thickness was measured with use of a digital film thickness meter, and a
specific resistance was calculated from these. The specific resistance
was calculated based on the following formula, and the unit was
represented by Ωcm. Specific resistance (Ωcm)=sheet
resistance (Ω)×film thickness (cm)

[0118]10. Heat Resistance

[0119]After the test piece prepared in 8. was thermally treated in a hot
air oven at 60° C. for 500 hours, the close adhesiveness and the
pencil hardness of the conductor were evaluated.

[0120]11. Humidity Resistance

[0121]After the test piece prepared in 8. was thermally treated in a
thermohygrostat at 60° C. with a relative humidity of 95% RH for
500 hours, the close adhesiveness and the pencil hardness of the
conductor were evaluated.

[0122]12. Heat Shock Resistance

[0123]The test piece prepared in 8. was left to stand in environments of
-40° C. and 70° C. each alternately for one hour with use
of a heat shock tester. After the test piece was left to stand for a sum
of 500 hours, the close adhesiveness and the pencil hardness of the
conductor were evaluated.

[0124]13. Coldness Resistance

[0125]After the test piece prepared in 8. was left to stand at -40°
C. for 500 hours, the close adhesiveness and the pencil hardness of the
conductor were evaluated.

[0126]14. Close Adhesiveness

[0127]With use of the test piece prepared in 8., the close adhesion
property was evaluated by a checker board cellotape (registered
trademark) exfoliation test according to JIS K-5600-5-6: 1991. Here, the
number of cuts in each direction of the lattice pattern was set to be 11,
and the cutting interval was set to be 1 mm. The notation of 100/100
shows that there was no exfoliation and the close adhesiveness is good,
whereas the notation of 0/100 represents that the whole was exfoliated.

[0128]15. Pencil Hardness

[0129]The test piece prepared in 8. was put on an SUS304 plate having a
thickness of 2 mm, and measurement was made according to JIS K 5600-5-4:
1999. Determination was made by the presence or absence of exfoliation.

[0130]16. Gel Fraction Ratio

[0131]The gel fraction ratio within the soluble solid component in the
conductive paste was determined as follows. The paste was filtered with
use of a filter paper 5th-kind A and a coating film was formed on a
polypropylene film (having a dried film thickness of 8 to 10 μm) with
use of the filtrate. The coating film was exfoliated after a treatment at
80° C. and for 30 minutes, so as to measure the weight thereof
(this weight is assumed to be W1). This was dissolved into a solution of
toluene/2-butanone=50/50 parts by weight, and the unsolved fraction was
separated to measure the weight thereof (this weight is assumed to be
W2). The gel fraction ratio within the soluble solid component was
calculated as being W2/W1.

[0132]17. Evaluation of Electrolytic Plating Property

[0133]As a pseudo electrolytic plating solution, an aqueous solution of
sulfuric acid with pH 1 was used, and the test piece prepared in 8. was
dipped at 25° C. for 4 hours, so as to measure whether there is no
change in the close adhesiveness and the pencil hardness of the paste
from those of the initial one. Determination was made by the presence or
absence of the change.

[0134]18. Evaluation of Non-Electrolytic Plating Property

[0135]As a pseudo electrolytic plating solution, an aqueous solution of
sodium hydroxide with pH 12.5 was used, and the test piece prepared in 8.
was dipped at 70° C. for 2 hours, so as to measure whether there
is no change in the close adhesiveness and the pencil hardness of the
paste from those of the initial one. Determination was made by the
presence or absence of the change.

[0136]19. Evaluation of Close Adhesiveness after Electrolytic Plating

[0137]The test piece prepared in 8. was subjected to electrolytic plating,
and the fabricated circuit was subjected to measurement of close
adhesiveness by the method of 14. Evaluation was made by an exfoliation
test. Similarly, this circuit was exposed to the environment test of 10
to 13, and the close adhesiveness test was carried out by the method of
14. to perform evaluation.

[0138]20. Evaluation of Close Adhesiveness after Non-Electrolytic Plating

[0139]The test piece prepared in 8. was subjected to non-electrolytic
plating, and the fabricated circuit was subjected to measurement of close
adhesiveness by the method of 14. Evaluation was made by an exfoliation
test. Similarly, this circuit was exposed to the environment test of 10
to 13, and the close adhesiveness test was carried out by the method of
14. to perform evaluation.

Synthesis Example 1

Synthesis of Polyester Resin I

[0140]In the known polyester polymerization method, a reaction vessel was
loaded with 238 parts by weight of terephthalic acid dimethyl ester, 238
parts by weight of isophthalic acid dimethyl ester, 9.6 parts by weight
of trimellitic anhydride, 186 parts by weight of ethylene glycol, 208
parts by weight of 2,2-dimethyl-1,3-propanediol, and 0.17 part by weight
of tetrabutyl titanate, and an ester exchange reaction was carried out at
180° C. to 230° C. for 8 hours. Subsequently, the pressure
of this reaction system was reduced to 5 mmHg in 30 minutes, and the
temperature was raised to 250° C. during this process. Further, a
condensation polymerization reaction was carried out under 0.3 mmHg and
at 250° C. for 30 minutes. The reduced viscosity of the obtained
polyester was 0.61 dl/g. Next, nitrogen gas was introduced to this
reaction system, and the reaction vessel was loaded with 399 parts by
weight of ε-caprolactone. After the reaction system was
homogenized, the resultant was heated at 220° C. for 2 hours, so
as to obtain a copolymerized polyester. The composition of the obtained
polyester resin was determined as terephthalic acid/isophthalic
acid/trimellitic acid//ethylene glycol/neopentyl
glycol//ε-caprolactone=49/49/2//55/45//140 (molar ratio) by
1H-NMR measurement. Also, the reduced viscosity was 1.2 dl/g; the
number-average molecular weight was 30,000; the acid value was 0.7
mgKOH/g; and the glass transition temperature was -18° C. The
composition and the physical properties of the polyester resin I are
shown in Table 1.

Synthesis Examples 2 to 5

Synthesis of Polyester Resins II to V

[0141]Polyester resins II to V were synthesized in the same manner as in
the synthesis example 1. The composition and the physical properties of
the polyester resins II to V are shown in Table 1.

Synthesis Example 6

Synthesis of Polyester Diol a

[0142]A reaction vessel equipped with a thermometer, a stirrer, and a
Liebig cooling tube was loaded with 97 parts by weight of terephthalic
acid dimethyl ester, 97 parts by weight of isophthalic acid dimethyl
ester, 82 parts by weight of ethylene glycol, and 92 parts by weight of
2,2-dimethyl-1,3-propanediol, and further, 0.1 part by weight of
tetrabutoxy titanate was added as a catalyst. The reaction was carried
out under an ordinary pressure at 240° C. for about 4 hours, and
the produced water was removed by distillation. Subsequently, the
pressure was reduced at 245° C. for about 10 minutes, so as to end
the reaction. The composition ratio (molar ratio) of the obtained
polyesterdiol (a) was determined as terephthalic acid/isophthalic
acid/ethylene glycol//2,2-dimethyl-1,3-propanediol=50/50//43/57, and the
hydroxyl value was 62 mgKOH/g. The composition and the physical
properties of the polyester diol a are shown in Table 2.

Synthesis Examples 7 and 8

Synthesis of Polyester Diols b and c

[0143]Polyester diols b and c were synthesized in the same manner as in
the synthesis example 1. The composition and the physical properties of
the polyester diols b and c are shown in Table 2.

Synthesis Example 9

Synthesis of Polyurethane Resin I

[0144]To 133 parts by weight of methyl ethyl ketone

[0145](hereafter referred to as MEK) and 133 parts by weight of toluene
(hereafter referred to as TOL), 100 parts by weight of polyesterpolyol
(a) sufficiently dried in advance, 150 parts by weight of ODX-688
(aliphatic polyester diol, number-average molecular weight of 2000,
manufactured by Dainippon Ink Chemical Industry Co., Ltd.) and 5 parts by
weight of 1,6-hexanediol were added. Further, 75 parts by weight of
4,4'-diphenylmethanediisocyanate and 0.1 part by weight of dibutyltin
dilaurylate as a catalyst were added, and reaction was carried out at
80° C. for 4 hours. Subsequently, the solution was diluted with
MEK: 504 parts by weight, so as to obtain a polyurethane resin I. The
composition and the physical properties of the polyurethane resin I are
shown in Table 3.

Synthesis Examples 10 and 11

Synthesis of Polyurethane Resins II to IV

[0146]Polyurethane resins II to IV were synthesized in the same manner as
in the synthesis example 1. The composition and the physical properties
of the polyurethane resins II to IV are shown in Table 3.

[0163]A mixture of conductive powder A (56.0 parts by weight), polyester
resin I (8.2 parts by weight), vinyl chloride-vinyl acetate resin I (3.4
parts by weight), curing agent I (4.5 parts by weight), and organic
solvent was passed through a chilled three-roll kneader to perform
dispersion. The obtained silver paste was printed, dried, and evaluated
by the method described in the above 8. Even by a heat treating condition
with a relatively low temperature of 80° C. and a short period of
time of 30 minutes in an oven, the coating film had a good physical
property with a specific resistance of 4.0×10-4 Ωcm, a
close adhesiveness of 100/100, and a pencil hardness of HB. Also, the
plating property was good. After an environment load was given, the
coating film exhibited almost the same good physical property as the
initial characteristics regarding heat resistance, humidity resistance,
heat shock resistance, and coldness resistance. The compounding, the
paste characteristics, and the coating film physical property of Example
1 are shown in Table 4.

Examples 2 to 9

[0164]Silver pastes of Examples 2 to 9 were prepared in the same manner as
in Example 1, and printed, dried, and evaluated by the method described
in the above 8. The compounding, the paste characteristics, and the
coating film physical property of Examples 2 to 9 are shown in Table 4.
In each of the Examples, even by a heat treating condition with a
relatively low temperature of 80° C. and a short period of time of
30 minutes in an oven, the coating film had a good physical property.

Comparative Examples 1 to 8

[0165]Silver pastes of Comparative Examples 1 to 8 were prepared in the
same manner as in Example 1, and printed, dried, and evaluated by the
method described in the above 8. The compounding, the paste
characteristics, and the coating film physical property of Comparative
Examples 1 to 8 are shown in Table 5. Comparative Example 1 is an example
in which vinyl chloride-vinyl acetate resin is not used, and blocked
isocyanate blocked with oxime is used as a curing agent. Comparative
Example 2 is an example in which flaky silver powder is used; vinyl
chloride-vinyl acetate resin is not used; and blocked isocyanate blocked
with oxime is used as a curing agent. Comparative Example 3 is an example
in which flaky silver powder is used, and a curing agent is not used.
Comparative Examples 4 and 5 are respective examples in which a high-Tg
polyester resin and a high-Tg polyurethane resin are used. Comparative
Example 6 is an example in which flaky silver powder is used, and the
amount of the conductive powder is extremely small. In Comparative
Examples 1 to 6, in each case, the coating film was inferior in humidity
resistance after electrolytic plating, and a good coating film physical
property was not obtained after non-electrolytic plating. Comparative
Example 7 is an example in which the curing agent was changed to blocked
isocyadnate blocked with oxime in Example 1; however, the coating film
was inferior in the close adhesiveness after the environment load test
both after electrolytic plating and after non-electrolytic plating.
Comparative Example 8 is an example in which vinyl chloride-vinyl acetate
resin is not used; a high-Tg polyester resin is used; and blocked
isocyanate blocked with oxime is used as a curing agent. In Comparative
Example 8 also, the coating film was inferior in humidity resistance
after electrolytic plating, and a good coating film physical property was
not obtained after non-electrolytic plating.

Examples 10 to 12

[0166]Examples 10 to 12 were carried out in the same manner as in Example
1 except that the compounding of the paste was changed as described in
Table 6, and that the insulating substrate was changed to a
polycarbonate/ABS resin substrate having a thickness of 500 μm. In
each of the Examples 10 to 12, even by a heat treating condition with a
relatively low temperature of 80° C. and a short period of time of
30 minutes in an oven, the coating film had a good physical property. The
compounding, the paste characteristics, and the coating film physical
property of Examples 10 to 12 are shown in Table 6.

Comparative Examples 9 to 11

[0167]Comparative Examples 9 to 11 were carried out in the same manner as
in Example 1 except that the compounding of the paste was changed as
described in Table 6, and that the insulating substrate was changed to a
polycarbonate/ABS resin substrate having a thickness of 500 μm. The
compounding, the paste characteristics, and the coating film physical
property of Comparative Examples 9 to 11 are shown in Table 6.
Comparative Example 9 is an example in which a high-Tg polyester resin is
used, and a curing agent is not used. Comparative Example 10 is an
example in which a high-Tg polyester resin is used. Comparative Example
11 is an example in which a high-Tg polyurethane resin is used. In each
of the Comparative Examples 9 to 11, the coating film was inferior in
humidity resistance after electrolytic plating, and a good coating film
physical property was not obtained after non-electrolytic plating.

[0168]The conductive paste of the present invention was printed as an
antenna pattern by the pad printing process shown in FIG. 2 on a housing
molded with use of a PC/ABS resin as a resin having a low heat resistance
temperature, and was thermally cured at 80° C. for 30 minutes.
Further, by an electrolytic plating process shown in FIG. 3, a conductive
layer having a plating construction shown in FIG. 5 was formed thereon.
The electrolytic plating process is carried out in the order from (1)
through to (12).

[0169](1) An object of plating is immersed into a degreasing liquid, so as
to perform degreasing.

[0170](2) Next, the resultant is washed with cleaning water.

[0171](3) Next, in order to remove oxide film of the conductive powder
contained in the conductive paste of the present invention, the resultant
is immersed into an acid active treating solution.

[0172](4) Next, the resultant is washed with cleaning water.

[0173](5) Next, the resultant is immersed into an electrolytic Cu plating
solution, and an electric current is applied to the conductive paste
layer serving as an object of plating, so as to deposit Cu.

[0174](6) Next, the resultant is washed with cleaning water.

[0175](7) Next, in order to remove oxide film of the Cu plated film, the
resultant is immersed into an acid active treating solution.

[0176](8) Next, the resultant is washed with cleaning water.

[0177](9) Next, the resultant is immersed into an electrolytic Ni plating
solution, and an electric current is applied to the Cu plated layer, so
as to deposit Ni.

[0178](10) Next, the resultant is washed with cleaning water.

[0179](11) Next, the resultant is immersed into an electrolytic Au plating
solution, and an electric current is applied to the Ni plated layer, so
as to deposit Au.

[0180](12) Next, the resultant is washed with cleaning water.

[0181]FIG. 6(a) is a perspective view of a notebook type personal computer
41 on which a housing-integrated type antenna circuit is mounted, where a
housing-integrated type antenna circuit 44 is mounted on the outside of
the upper lid (housing) 43 in which the display 42 is disposed. FIG. 6(b)
is a perspective view in which only the housing-integrated type antenna
circuit 44 mounted on the notebook type personal computer 41 is taken
out, where the antenna circuit is incorporated in the housing.

[0182]For the pad printing process of Example 13, the method shown in FIG.
2 was used as an example. Here, first, a (desired) antenna pattern 21
made of the conductive paste was prepared, and then this antenna pattern
21 was subjected to first printing on the convex part of the pad 22, and
thereafter the antenna pattern 21 on the convex part of the pad 22 was
subjected to second printing at a predetermined position on an insulating
substrate 23 such as a housing. Also, as a construction of plating shown
in FIG. 5, a coating film 32 formed from the conductive paste was formed
on an insulating substrate 31 constituting a housing, and subsequently,
each film of Cu 33, Ni 34, and Au 35 was successively formed thereon, so
as to construct a plated layer made of three films.

Example 14

[0183]The conductive paste of the present invention was printed as an
antenna pattern by the pad printing process shown in FIG. 2 on a housing
molded with use of a PC/ABS resin as a resin having a low heat resistance
temperature, and was thermally cured at 80° C. for 30 minutes.
Further, by a non-electrolytic plating process shown in FIG. 4, a
conductive layer having a plating construction shown in FIG. 5 was formed
thereon. The non-electrolytic plating step is carried out in the order
from (1) through to (16).

[0184](1) An object of plating is immersed into a degreasing liquid, so as
to perform degreasing.

[0185](2) Next, the resultant is washed with cleaning water.

[0186](3) Next, in order to remove oxide film of the conductive powder
contained in the conductive paste of the present invention, the resultant
is immersed into an acid active treating solution.

[0187](4) Next, the resultant is washed with cleaning water.

[0188](5) Next, the resultant is immersed into a catalyst imparting
treating solution in order to impart a catalyst.

[0189](6) Next, the resultant is washed with cleaning water.

[0190](7) Next, the resultant is immersed into a non-electrolytic Cu
plating solution to deposit Cu.

[0191](8) Next, the resultant is washed with cleaning water.

[0192](9) Next, the resultant is immersed into a catalyst imparting
treating solution in order to impart a catalyst.

[0193](10) Next, the resultant is washed with cleaning water.

[0194](11) Next, in order to prevent deposition outside of the pattern,
the resultant is immersed into a post-activator treating solution to
remove the catalyst adhering to the outside of the pattern.

[0195](12) Next, the resultant is washed with cleaning water.

[0196](13) Next, the resultant is immersed into a non-electrolytic Ni
plating solution to deposit Ni.

[0197](14) Next, the resultant is washed with cleaning water.

[0198](15) Next, the resultant is immersed into a non-electrolytic Au
plating solution to deposit Au.

[0199](16) Next, the resultant is washed with cleaning water.

[0200]FIG. 6(a) is a perspective view of a notebook type personal computer
41 on which a housing-integrated type antenna circuit is mounted, where a
housing-integrated type antenna circuit 44 is mounted on the outside of
the upper lid (housing) 43 in which the display 42 is disposed. FIG. 6(b)
is a perspective view in which only the housing-integrated type antenna
circuit 44 mounted on the notebook type personal computer 41 is taken
out, where the antenna circuit is incorporated in the housing.

[0201]For the process of the pad printing of Example 14, the method shown
in FIG. 2 was used in the same manner as described in Example 13. Also,
as a construction of plating shown in FIG. 5, a coating film 32 formed
from the conductive paste was formed on an insulating substrate 31
constituting a housing in the same manner as described in Example 13, and
subsequently, each film of Cu 33, Ni 34, and Au 35 was successively
formed thereon, so as to construct a plated layer made of three films.